Apparatus for handling and cooling foundry sand

ABSTRACT

The invention disclosed herein relates to a novel method of handling and cooling foundry sand. The method includes the steps of preparing a quantity of the foundry sand, conveying a portion of the sand to a molding machine and forming molds therefrom, casting a metal into the molds, breaking up the molds, and mixing the unused sand with the used sand. Only a portion of the usedunused sand mixture is subsequently mulled, the remainder being retained in a storage tank for subsequent cooling. By using this method, the temperature of the foundry sand can be controlled and the use of costly cooling apparatus can be eliminated.

United States Patent Schumacher Oct. 2, 1973 APPARATUS FOR HANDLING AND l,808,366 6/l93l McWane 164/5 2,478,46l 8/l949 Connolly .1 164/5 x COOLING FOUNDRY SAND 75 In tor: 05 h S. S h h C' t', l ven inner c umac er, lncmna P imary xaminerJ. Spencer Overholser Assistant Examiner-John E. Roethcl [73] Assignee: International Minerals & Chemical An -Edwa d B. Evans ct al.

Corporation, Cincinnati, Ohio [22] Filed: June 22, I971 5 ABSTRACT PP NOJ 1551589 The invention disclosed herein relates to a novel Related Us. Application Dam method of handling and cooling foundry sand. The [60] Division or SCI. N0. 839 339 July 7 1969 Pat. NO. method includes the l of prepfring a quantity Ofthc 3,604,493, which is a coritinuation-in part oi Ser. No. foundry Sand conveymg a Porno of the sand to 3 H4339 March 19 1968 Pat N0 3 461,941. molding machine and forming molds therefrom, casting a metal into the molds, breaking up the molds, and mix- 1521 US. Cl 164/270, 164/5, 164/412 ihg the unused Sand with the used Sahdonly a Portion 51 1m. 01. 822C 5/16, B22d 47/02 of the used-uhused Sand mixture is Subsequently [58] Field of Search 164/5 270 412 mulled the remainder being retained in a Storage tank for subsequent cooling. By using this method, the tem- [56] References Cited perature of the foundry sand can be controlled and the UNITED STATES PATENTS use of costlycooling apparatus can be eliminated. 3,627,024 12/1971 Schumacher 164/270 1 Claim, 1 Drawing Figure ADDlTlVES f SHAKE OUT DIVIDER 6 CASTING TANK MACHINE MOLDING MULLER MACHINE PATENIED ADDITIVES Y SHAKE OUT DIVIDER f6 CASTING TANK MACHINE MOLDING MULLER MACHINE INVENTOR.

Joseph 5. Schumac/rr APPARATUS FOR HANDLING AND COOLING FOUNDRY SAND CROSS REFERENCE TO RELATED APPLICATIONS This application is a division of US Pat. application Ser. No. 839,339 now US. Pat. No. 3,604,493, which in turn is a continuation-in-part of US. Pat. application Ser. No. 714,339, now US. Pat. No. 3,461,941.

This invention relates to a method for handling foundry sand. More particularly, it relates to a method for handling foundry sand wherein the temperature of the sand is cooled to a desired temperature after it has been used.

In a recent article entitled Survey of Methods to Cool I-Iot Sand written by A. J. Filipovitch, and appearing at page 92 in V]. 95, No. of the October, 1967 issue of Foundry magazine, a survey of the methods used by 21 l foundries to cool foundry sand is presented. The author reports that the most frequently used methods for cooling foundry sands include costly apparatus such as muller, belt aerators, rotary screens, fluidizing units, perforated cooling elevators and cooling tables. He states that all of the methods rely upon the use of water to lower the temperature of the hot, used sand to about 170 F. and then on air cooling to further reduce the temperature. The optimum temperature to which the sand must be cooled to is about room temperature.

If foundry sand which has been used is not cooled before it is reused, several problems arise. It is pointed out in the article referred to previously that hot sand is very unstable and its properties change as its moisture evaporates. This variable condition causes poor pattern draws resulting in inferior casting quality. It is also known that variations in moisture, even though they appear inconsequential, can cause radical changes in compressive strength, permeability and flowability. These changes can lead to poor finish, defective castings and increased scrap. If too much moisture is added, the sand tends to agglomerate. Another problem that is present is that when hot sand is conveyed, it does not flow very well and tends to pack and agglomerate in the equipment, tanks, conveyors and elevators. The constant and rapid loss of moisture by evaporation as the sand cools creates in a quantity of sand a condition of dryness on the surface to wet in the center. Uniformity of properties is a condition to quality. It does not exist in hot sand.

An important object of my invention is to provide a method for cooling foundry sand to approximately room temperature without the need for using expensive and complicated cooling equipment. Another important objective of my invention is to provide a method for cooling foundry sand which does not depend upon air or water as the cooling medium. A still further objective of this invention is to provide a foundry sand handling system wherein the composition of the foundry sand can be easily controlled and the compositional variations are minimized.

In the casting of metals into sand molds, the amount of sand used to form a mold is usually expressed as a function of the amount of metal to be poured into it. This relationship is called the sand to metal ratio. For example, sufficient sand can be used for the mold to give a sand to metal ratio of from three to one to to one. While these ratios are frequently used, others are oftentimes used too. A common ratio used is a ratio of about six to one. That is, a mold is formed which consists of 6 pounds of sand for each pound of metal to be cast.

Foundry sand is, of course, not sand alone but contains additional constituents such as clays and/or carbons and/or other additives and/or temper water. Carbons in common use are powdered coal, coal tar, pitch, asphalt, graphite and coke. Other additives can be added such as celluloses, cereal binders, etc. After one or more molding operations new sand and/or clays and- /or carbons can be added to the used sand to replace the portion of the original sand which has been made unuseable. Temper water is also frequently added in minor amounts. The following is a typical table which shows the amount of additives which usually must be added after the batch of sand has been used. This table is for ferrous metals other than steel. Other data for non-ferrous metals, steel and ductile metals is known to those in the foundry industry.

Table l SUGGESTED ADDITIVE REQUIREMENTS PER MULLER LOAD OF 2000 POUNDS Ratio Clay Sand/Metal Bentonite Carbons New Sand pounds pounds pounds 3/1 18.8 16. 100. 4/1 14.4 1 1.9 5/1 1 1.3 9.5 60 6/1 9.41 8.0 50 8/1 7.15 6.03 37.5 10/1 5.65 4.75 30.0 12/1 4.71 4.00 25.0 14/1 4.05 3.43 21.4 16/1 3.60 3.03 18.7 18/1 3.15 2.66 16.6 20/1 2.83 2.40 15.0

As it can be seen from this table, it requires about 34.8 pounds of new clay and additives plus pounds of new sand to reconstitute the molding sand for reuse at a sand to metal ratio of three to one. However, at a ratio of 20 to one it requires only 5.2 pounds of new clay and additives, plus 15 pounds of new sand to reconstitute it at this ratio.

I have discovered that if one desires to operate a sand system at a normal sand to metal ratio of about four to one to six to one that conventional cooling methods can be eliminated if a batch of foundry sand is mixed so as to provide a 20 to one ratio, the molds are made, for example, on a four to one to six to one ratio, and if immediately after the molds are used and broken up, the remaining unused cool portion of the mixed sand is mixed with the hot used sand. By mixing the unused sand with the used sand, the temperature of the combination of sand islowered so that a portion of the batch can be reused without further cooling, after temper water and/or additives have been added and it has been remulled. No other cooling step is needed. Moreover, sand used in this manner is easy to reconstitute because the amount of additives lost per molding cycle expressed as a percent of the total batch is very small. It can be seen, therefore, that my invention provides a novel method of cooling foundry sand while at the same time it provides a method for controlling the composition of the foundry sand and for minimizing variations in composition.

I have found that it is generally desirable to cool the used sand as close to ambient temperature as possible after the molds are shaken out and prior to the mulling and reconstituting of the sand. While ambient temperature is preferred, sand at a temperature of 120 F. can be used. However, it is desirable to cool the sand to below 120 F. to obtain the best mixing results. Most clays are difficult to wet and plasticize when the temperature is over 120 F. If sands are prepared at l F. then drying out will rapidly occur due to evaporation till ambient temperature is reached. Moisture losses change the properties of the molding sand. A consistent molding media is desired for best results. Therefore, I have found that the most efficient mixing is achieved when the sand is at ambient temperature. The amount of sand which must be added after shakeout in order to obtain a mixture of used and unused sand at a particular temperature is, of course, dependent upon the temperature of and the amounts of the used and unused sands. I have found that the approximate amount of unused sand which must be added can be calculated in the following way.

An estimation of the temperature of the sand at shakeout can be made if it is assumed that all the heat evolved from the hot metal is transferred to the sand. The temperature of the metal in an average pouring for iron is about 2,600 F. The heat evolved can be calculated from the following formula y cbft tifl lwhere cp mean specific heat of pure iron at 2,600 F., t shakeout temperature, and 60 standard ambient temperature. No heat of solidification has been included because of the different metals which might be used. The following table shows the heat evolved at the indicated shakeout temperature when the pouring temperature is 2,600 F.

TABLE II Shakeout Temp. of Heat Evolved-BTU These results can be plotted on a graph so that the intermediate values can be easily obtained.

Knowing the heat evolved from the metal and assuming that all of this heat is transferred to the sand then the temperature of the sand at various shakeout temperatures can be calculated. The formula that should be used is H Cp J: sand weight per pound of iron x (t60) where H is the heat evolved from the iron, Cp is the heat for SiO, for t-60, and t sand temperature at shakeout. The following tables show the temperature of the sand at various metal shakeout temperatures.

TABLE III 20 to 1 Sand to Metal Ratio Casting Shakeout Temp. Sand Temperature Casting Shakeout Temp. Sand Temperature 180 F.

2000 F. 300 F. 220 F. 1200 F. 260 F.

TABLE V 4 to l Sand to Metal Ratio Casting Shakeout 'lcmp. Sand Temperature Again it was assumed that the pouring temperature of the metal was 2,600 F. The above temperatures can be plotted so that intermediate temperatures can be determined quickly. The above calculated sand temperatures assume that there is no moisture in the sand. However, in practice there is usually between three to five percent of water in the sand. The evaporation of this moisture will cool the sand still further. For exampic, at a 10 to one sand to metal ratio the sand, at shakeout temperatures, will be cooled about 53 F. for each one percent of moisture evaporated. In most foundries the shakeout temperature is between 1,000 and l,300 F. Therefore, in order to have sand at not more than F. as it goes into the muller, the sand to metal ratio at this point must be between 10 to one and 20 to one. A 10 to one mixture will provide this temperature because about three percent of moisture has been evaporated.

The amount of sand actually used to form the mold can be any ratio but common values are a sand to metal ratio of four to one to about six to one.

Conventional foundries usually have a muller, a sand storage bin, a molding machine and some means for breaking up the used sand molds and separating the castings. Such a conventional sand system with the conveyors, muller, etc. is shown at pages 9 and 10 of the aforementioned foundry magazine. In my system any number of the various kinds of batch or continuous mullers, molding machines and shakeout mechanisms can be used. Such devices are well known to those in the art and the use of any particular one forms no basis of invention of this application and is not required in my process.

The following is an example of how my process has been successfully practiced at a foundry where expensive equipment had previously been used to cool its foundry sand.

The muller used at the foundry was a continuous muller, that is, a continuous flow of sand was introduced into the muller and a continuous flow of mulled sand was discharged from the muller. The approximate composition of sand used was 86 percent silica, 6 percent clay, 4 percent carbons and 4 percent water. Periodic additions of clays, carbons and new sand, calculated according to the figures shown in Table I were made to the sand at the muller during the casting cycle. A large amount of sand was prepared. However, the molds were made on a four to one sand to metal ratio. The metal cast was malleable iron having an approximate composition of 3.5 percent total carbon and 0.6 percent Si. The sand which was not used to form the molds was conveyed to a storage tank. After the metal was cast, the castings and molds were conveyed to a shakeout station and the molds broken. Immediately after the castings were separated from the broken molds at the shakeout station, about 16 parts of cool sand at ambient temperature from the storage tank were added to the hot used sand. The temperature of the used sand prior to the addition of the unused sand was over 350 F. By the time the mixture of hot used sand and cool unused sand has been transported by a conventional conveyor to a second storage bin, a distance of approximately 200 feet, the temperature of the batch was approximately 100 F. After this, the sand was conveyed to the muller. After the mulling process, the temperature of the sand was approximately 90 F. No additional cooling of the sand was provided. It was then conveyed to the first storage tank. After using this process for several weeks, it was apparent that the quality of the molds and of the finished castings was greatly improved over the process previously practiced which included conventional sand cooling apparatus. Moreover, it was found that it was much easier to control the composition of the sand and there was much less variation in the composition. Additionally, it was found that the sand was much easier to handle because its flowability was improved. Another unexpected result was that air pollution was drastically reduced. It is believed that expensive air cleaning equipment will also be eliminated by using my process.

I have found that further advantageous results can be obtained if the additives necessary to replace those that have been destroyed during the molding process are added at the shakeout point. At this point it is easier to determine the amount of new sand, clays and carbons which are needed because the amount of sand actually used during the molding process is known. In most foundries the sand to metal ratio remains constant over a period of several hours. Therefore, the additions would be constant over the same period of time and could be gauged for example by color coding the molds to indicate that a particular sand to metal ratio is being used. Once the sand to metal ratio and the weight of the sand used or metal poured is known, then the amount of clays, new sand and carbons can be ascertained for ferrous metals by referring to Table I hereof.

In some existing foundries where my process could advantageously be practiced it has been observed that the muller capacity of the existing mullers has been insufficient to mull the quantity of sand required for both molding and cooling. I have found that in these foundries my process can be employed if the portion of sand which could not be mulled because of the insufficient mulling capacity is bypassed around the muller. Of course, as desired, the quantity of sand bypassed around the muller can be varied as desired.

Referring now to the drawing, there is shown there my cooling process wherein a portion of the sand can be bypassed around the muller if desired.

In the drawing, muller 1 can be any type of conventional sand muller such as the continuous one described in U. S. Pat. No. 3,408,052. Other mullers, continuous or batch, could also be used. Likewise, the molding machine 2, shakeout 3, additive adding machine 4 and tank 6 may be of conventional design and are all very well known in the foundry art. The divider may be one of those shown in my U.S. Letters Pat. No. 3,627,024, or others which are adapted for that specific purpose. Connecting these various machines in operable relationship are suitable conveyors, not shown, but

which are illustrated by arrows. These arrows show the direction of sand travel during the molding operation.

During a typical cycle of operation sand exists in the muller l and is conveyed to the molding machine 2, where sand molds are then formed. A sufficient quantity of sand is conveyed so that molds are formed having a sand to metal ratio of at least 3. At this point, there resides in tank 6, a quantity of sand equal or greater than 10 times the weight of metal to be cast. After the castings and molds leave the machine 2, they are separated at the shakeout 3. At this point additives are added from the additive machine 4. The amount of additives added is based upon the weight of sand used and the sand to metal ratio. For instance, if the amount of sand was 2,000 pounds and the sand to metal ratio was 3 to 1 then referring to Table I it can be seen that 18.8 pounds of clays, 16 pounds of carbons, and pounds of new sand must be added.

It is important that the required additives be added before the hot sand-cool sand mixture is split and a portion sent to the muller and the other portion sent to bypass the muller. Preferably the additions should be made at the shakeout, for the reasons previously discussed. If instead, the additions are made at the muller, there will be no easy way for deterring the quantity of additives necessary for it will not be known whether or not the sand being mulled was the sand used for molding and, hence, it would not be known what amounts of the various additives must be used.

As the hot sand leaves the shakeout 3 with the required additives, a sufficient quantity of cool sand from the tank 6 is discharged onto the hot sand. At this point mixing equipment such as known in the prior art may be used to mix the hot and cool sand.

The hot and cool sand mixture reaches the divider 5 where a portion of the sand is divided and deposited in the tank 6. The remaining portion, sufficient to form the number of desired molds, is mulled, with or without adding temper water, and the cycle starts again.

Having thus described my invention I claim:

1. A foundry system for mulling, handling, molding and cooling foundry sand comprising in combination,

a sand muller for mulling said foundry sand,

molding means for forming said foundry sant into molds,

casting means for casting metal into said molds,

shakeout means for separating said castings and said molds,

first sand conveyor means connecting said muller to said molding machine,

second sand conveyor means connecting said molding machine to said shakeout machine,

third sand conveyor means for connecting said shakeout means to said muller,

means for dividing said sand on said third conveyor into a plurality of portions,

a storage tank,

fourth conveyor means connecting said dividing means to said storage tank, and

fifth conveyor means for connecting said storage tank to said third conveyor means. 

1. A foundry system for mulling, handling, molding and cooling foundry sand comprising in combination, a sand muller for mulling said foundry sand, molding means for forming said foundry sant into molds, casting means for casting metal into said molds, shakeout means for separating said castings and said molds, first sand conveyor means connecting said muller to said molding machine, second sand conveyor means connecting said molding machine to said shakeout machine, third sand conveyor means for connecting said shakeout means to said muller, means for dividing said sand on said third conveyor into a plurality of portions, a storage tank, fourth conveyor means connecting said dividing means to said storage tank, and fifth conveyor means for connecting said storage tank to said third conveyor means. 